Rotary steam engines are well known in the art. Early constructions may be found in patents to Fisher U.S. Pat. No. 137,065; Shepard U.S. Pat. No. 525,121; Taylor U.S. Pat. No. 597,793; Taylor U.S. Pat. No. 949,605; Gross U.S. Pat. No. 968,653; and Conklin U.S. Pat. No. 1,270,498. See also Plummer U.S. Pat. No. 2,454,006; Farrell U.S. Pat. No. 3,109,382; Eyer U.S. Pat. No. 3,236,187; Nardi U.S. Pat. No. 3,865,522 and Gardiner U.S. Pat. No. 4,393,829.
In this type of steam engine there is no reciprocating piston. Instead each piston is permanently attached to the rotating cylinder walls and moves continuously in one direction. The inner transverse edge of each piston engages and slides along the cylindrical surface of a stationary inner body. The inner body carries a plurality of rotatable elements (ordinarily one more than the number of pistons) mounted for rotation in a succession of cavities in the inner body.
The rotatable elements act to form the ends of the curved cylinders. The construction permits the piston on reaching the end of its stroke, to pass the rotatable element to move into the next cylinder.
The radially outermost part of each rotatable element forming the end of the cylinder is in steam tight sliding engagement with the rotating walls of the cylinder.
In order that the piston may pass the rotatable element, it is essential that the piston and the rotatable element be in a form which might be said to be roughly in the nature of paired gear teeth. Thus the piston would represent an internal tooth, designed to cooperate with external teeth on the rotatable element.
In some of the early forms disclosed in the prior art, it was considered desirable to gear the rotating part of the engine to the rotatable element in such manner that when the piston reached the rotatable element, the latter would be positively rotated by the gearing so that the piston would enter a complementary cavity in the rotatable element and thus to pass thereby. In other forms in the prior art, the piston came into positive engagement with one of the stationary blades of the rotatable element and forced the blade to rotate, thereby permitting passage of the piston into the next curved cylinder.
In all of the prior constructions, the shape of the piston and the shape of the blades of the rotatable elements did not provide for efficient passage of the piston past the rotatable element. There was a leakage of steam, excessive condensation, undue wear of the engaging portions, inefficiency in the location of the exhaust ports, inefficiency in the performance of the steam admission ports and inability to change the time of steam cut-off.
In my prior invention, U.S. Pat. No. 3,865,522, the piston was attached to the outer walls of the engine with its inner edge slideable along the cylindrical surface of the inner fixed body, generally in the form of a smaller gear tooth of different configuration. The rotatable element which permitted the passage of the piston had four blades generally in the shape of large gear teeth. At the root of adjacent blades, the opposed surfaces were shaped in the form of two small adjacent teeth designed to cooperate closely with the small tooth on the inner end of the piston. The major portion of each wall blade had substantially the reverse configuration of the walls of the piston.
Thus, as the piston came close to the face of the blade which was then acting as the end of the curved cylinder and with the exhaust port closed, the pressure generated between the piston and the blade wa usually sufficient to induce starting rotation of the blade. Immediately after the start of rotation, the tooth formation on the inner end of the piston reached its position of engagement in the previously referred to tooth formations that are at the roots of the adjacent blade surfaces. Thus the blade was started in its rotation by the rising pressure between the piston and the blade surface and was compelled to continue its rotation by the engagement of the small toothed end of the piston with the corresponding tooth formation between adjacent blades. If the pressure between the piston and blade was insufficient to start rotation, the piston engaged the blade at its outer end to compel rotation. The shape of the engaging surfaces was such that they rolled against each other until the small inner teeth took over.
There were two pistons spaced 180.degree. apart and three rotatable elements (each with four blades) spaced 120.degree. apart. Thus there was always at least one steam cylinder in operation and there was never be any position of dead center. As a result, the rotation of the outer part of the engine was continuous and the driving force provided by the steam was substantially uniform. The rotating outer part of the engine acted as a fly wheel and maximum torque was always available from 0 rpm to top speed.
My present invention differs from my prior invention and involves three basic changes. In the present invention, the outer housing is stationary and not rotational; the piston, which I refer to in this disclosure as a virtual piston, is a free floating piston and has no shaft. In my prior invention, it was confined by a shaft. Lastly, the valving in the cylinder head is distinct.
Broadly my invention is a positive displacement, single expansion true steam expander, like the tubine i.e., it has no compression cycle. The engine is designed to operate on saturated steam at moderate temperatures and pressures (475.degree. F. and 500 psi). At these temperatures, a 5% mixture of lubricating oil may be admitted to the steam directly. In general terms, my engine can be classified as a postive displacement turbine.
A steam turbine's longevity (20 years) is based on 100% fixed gap clearance; i.e., no metal to metal contact. The present invention has a fixed gap clearance of about 80%. The remaining components are pressure balanced which minimizes metal to metal contact.
The engine of the preferred embodiment has a high power/weight ratio (2 lbs./HP - least admission, 0.5 lbs./HP full full admission). It is equivalent to a 12 cylinder IC engine because there are 6 power strokes per revolution. Furthermore, it has a wide power range--0.05--1 megawatt and its thermal efficiency is not a first order function of RPM.
In the present invention, cylinder heads are fixed to the outer wall of the engine. The inner edge of the cylinder head has a fixed gap and discrete seal which is slidable along the cylindrical surface of a rotatable power shaft assembly, which shaft has a plurality of nests. Received in each of the nests is a virtual piston having lobes which allow free movement of the pistons in the nests, the outer edges of the lobes in sliding engagement with the inner surface of the nest and the inner surface of the fixed outer wall of the engine. Further, the opposed surface defined by adjacent lobes cooperates closely with the outer surface of the cylinder head. Thus, the major portion of each piston lobe has substantially the reverse configuration of the walls of the cylinder head. However, the design is such that an acceleration/deceleration ramp is in the compression/ admission cycles
The virtual piston within the nest is balanced at all times (except when in contact with the cylinder head). Specifically, a seal on the cylinder head vertex effectively reduces the area on the face of contact about its axis of rotation within the nest but is imbalanced with reference to the center of rotation of the tri-nested power shaft assembly. Upstream of the cylinder head is an exhaust port. As the facing surface of a first lobe approaches the exhaust port, a chamber is defined by the inner surface of the stationary wall, the surface of the cylinder head opposing the facing surface of the lobe, the outer surface of the power transfer shaft and the surface of the lobe next preceeding the first lobe. As the first lobe passes the exhaust port, the exhausting ceases and compression commences in the newly defined volume. The shaft assembly continues to rotate in a counterclockwise direction, while clockwise rotation is imparted to the virtual piston by virtue of the compression building up in the diminishing volume. As rotation continues, the first lobe engages the opposed surface of the cylinder head.
The shaft assembly continues to rotate in the counterclockwise direction. The virtual piston always rotates in the clockwise direction. A new volume is defined on the other side of the cylinder head between the surface of the next preceeding lobe facing the opposed cylinder head surface, and the facing surface of the first lobe. Steam is introduced from the cylinder head into this volume tending to drive the free piston in a counterclockwise direction. The piston is unbalanced but cannot rotate in a counterclockwise direction because it is prevented from doing so at this time by contact with the vertex of the cylinder head. The force created by the introduction and expansion of the steam in the closed chamber continues to drive the shaft assembly in the same direction (ccw).
In the preferred embodiment, there are two cylinder heads spaced 180.degree. apart and three virtual pistons spaced 120.degree. apart. Thus, there is always at least one steam cylinder in operation and there never will be any postion of dead center. As a result, the rotation of the inner shaft assembly is continuous and the driving force provided by this stream is substantially uniform.